The invention relates to a pressure measuring apparatus, and more particularly, to an improvement of the surface structure of a seal diaphragm that separates a fluid to be measured from a pressure transmitting medium.
FIG. 6 is a sectional view illustrative of a construction of a generally used conventional pressure measuring apparatus.
As shown in FIG. 6, this conventional apparatus consists mainly of a detecting section 20 and a protecting section 30, and these sections are connected to each other through connecting pipes 16, 17. The detecting section 20 converts a pressure variation (differential pressure) of a fluid to be measured into an electric signal and outputs such electric signal. The protecting section 30, as will be described later, performs the function of protecting the detecting section 20 from excessively applied pressures.
Although some pressure measuring apparatuses are designed so that the detecting section 20 are arranged inside the protecting section 30, a pressure measuring apparatus having the detecting section 20 arranged outside the protecting section 30 as in FIG. 6 is advantageous in that the detecting section 20 is not affected by the temperature of the fluid to be measured even if the fluid to be measured is hot.
The protecting section 30 includes: bodies 31, 32; a protecting diaphragm 13; a seal diaphragm 10; an O ring 18; a cover 19; and a connecting pipe 23. Here, the bodies 31, 32 interpose the protecting diaphragm 13 therebetween on both the right and left side in FIG. 6, and connected to each other at the outer circumference or edge portions. The O ring 18, the cover 19, the connecting pipe 23, and the seal diaphragm 10 are provided in pair.
Also, on the bodies 31, 32 are recessed portions 11, 21, holes 14, 24, and holes 45, 55 formed so as to be symmetrical to each other. The recessed portion 11 is formed in conical form on the left side end of the body 31 so as to be coaxial with the body 31, the hole 14 passes through the body 31 along the line of axis, the hole 45 is opened in the vicinity of the outer circumference of the recessed portion 11 on one end, and it communicates with a not shown connecting space within the detecting section 20 while passing through the connecting pipe 16. The body 31 is formed into a wavy section on its right side end, and the seal diaphragm 10 having substantially the same wavy pattern is firmly secured to its edge portion so as to form a space with its right side end. The cover 19 is mounted on the right side of the body 31 through the O ring 18 that is disposed at the outer circumference further outward from the seal diaphragm 10. The connecting pipe 23 is connected to this cover 19.
The body 32 on the left side is constructed substantially in the same way, and silicone oil (a sealing fluid) serving as a pressure transmitting medium is loaded into the space that is in contact with the seal diaphragm 10 and into the spaces formed of holes 14, 24, recessed portions 11, 21, and holes 45, 55.
In the thus constructed pressure measuring apparatus, part of the fluid to be measured passes through the seal diaphragm 10, infiltrates into the silicone oil that serves as the pressure transmitting medium, and resides therein in the form of hydrogen gas, thus making accurate pressure measurement impossible. In some extreme case, there may be the risk of making pressure detection totally impossible.